The f
ine details of the electronic structure of iron-
based superconductors are responsi
ble for the complete loss of resistance at relatively high temperatures. Although the underly
ing mechanism of this phenomenon is not yet fully understood, the high-resolution measurements of the lowenergy electronic states may help to f
ind the answer. The results of such experiments for LiFeAs o
bta
ined
by angleresolved photoemission spectroscopy (ARPES) reveal the presence of sp
in-or
bit splitt
ing, a fundamental
interaction which is suggested to contri
bute to the pair
ing of electrons (see the Feature Article
by Borisenko et al., article no.
b.201600550" title="Link to external resource: http://doi.wiley.com/10.1002/pssb.201600550" target="_blank">1600550). The Fermi surface map (upper row of the cover pictures, third panel) shows that sp
in-or
bit coupl
ing lifts the degeneracy
in those positions where the electron-like pockets crossed
in the non-relativistic case. This
interaction converts the Fermi surfaces encircl
ing the corner of the Brillou
in zone to clearly separated
inner and outer electron pockets. The o
bservation that those electronic states which are split–most (centers of the middle and lower row panels) support the largest superconduct
ing gap argues for a relationship
between sp
in-or
bit coupl
ing and Cooper pair
ing
in iron-
based materials. [Adopted from Nature Phys. <
b>12
b>, 311 (2016).]